'China has committed to notable reductions and when a Chinese leader says "notable" he means it. China does not embark on plans unless it understands how it can be done and that is why it will take a little while for China to come up with numbers.'

USA

While praising the progress of China and India, which both have ambitions to make solar more competitive than coal, Stern said the main problem was now the USA:

'There is no other country in the world that has as strong a team as Obama's on science. The problem is US politics and can they deliver enough in time.

'The Waxman-Markey bill is a step forward and will bring the US by 2020 down to where they were in 1990. But it won't be there in time for Copenhagen.

'No-one wants to argue that the US doesn't have a great deal to do but at the same time we have to understand the constraints of US politics,' he said.

Green growth

'Can we grow and de-carbonise growth? Yes, we can with the right type of policies', says Stern.

'We are likely to set off a process of growth that is as dynamic as any we've seen in economic history precisely because the innovation and investment and change that is necessary is so strong and covers the whole economy.

'The transition to a low-carbon economy over the next four decades, if we get our policies right, will be among the most dynamic periods of growth in human history. And when we get there it will be more energy secure, quieter, cleaner, safer and more biodiverse.'

Copenhagen

'If you look at the kind of intentions that are on the table now, based on announced policies from the EU, China, Japan, India and what the US has on the cards with Waxman-Markey, if you put all those together we may be reducing from business as usual levels to around 48/49 gigatonnes of carbon by 2020.

'So we have about 4/5 gigatonnes to go to get under 44 gigatonnes by 2020. We don't have far to go. It is possible. What it needs is very strong and enlightened leadership and strong pressure from those who aren't leaders.'Useful linksLSE International Growth CentreSee also